Syntax : Functions

Functions

Piecewise

You’ve seen lots of this in lectures. Here’s an example copy and pasted from your assignment:

adjacentCoord :: Direction -> Coord -> Coord
adjacentCoord R (C x y) = C (x+1) y
adjacentCoord U (C x y) = C  x   (y+1)
adjacentCoord L (C x y) = C (x-1) y
adjacentCoord D (C x y) = C  x   (y-1)

Cases

Cases are just an extension of the piecewise definition. Cases use pattern matching, just like the piecewise definition. Using case statements allows for less repetition, but you are limited to matching only one variable.

Write adjacentCoord using a case statement.

Guards

Guards are similar to piecewise and case statements in that they check for something and then runs the corresponding code. The only way it differs is that guards involve a Boolean expression as opposed to a pattern.

Write the absolute value function using guards.

Where to use where statements

Where statements are used when there is a long block of code that you want to make shorter, or when an expression appears more than once.

Clean up the following embarassing code from my first year with where statement(s)

world :: DenseWorld -> DenseWorld
world denseWorld = denseWorld
    {theWorld = direction (antDirection denseWorld) denseWorld,
         minX = checkminX (xCoord (getCoord denseWorld)) denseWorld,
         maxX = checkmaxX (xCoord (getCoord denseWorld)) denseWorld,
         minY = checkminY (yCoord (getCoord denseWorld)) denseWorld,
         maxY = checkmaxY (yCoord (getCoord denseWorld)) denseWorld}

Is this Boolean, pattern or both?!

x > 3

True

otherwise

even 5

Even 5

Just Nothing